It is advantageous, particularly for planning and monitoring of catheter interventions, to use a three-dimensional model of a blood vessel system of a patient. Such a three-dimensional presentation is mostly intended to be reconstructed from a number of two-dimensional image recordings, especially x-ray recordings. In principle, it would be possible in such cases to calculate a 3D presentation from a number of two-dimensional projection images of vessels, especially with administration of contrast media. In everyday clinical practice, however, additional requirements are to be placed on the imaging of the blood vessel system. Thus, images are typically to be recorded within a small area of rotation of a C-arm system in order not to disturb the clinical workflow. For dose reduction, the number of projection images recorded is typically restricted as far as possible. Recording images of the blood vessel system is also made more difficult by the fact that vessels in the heart region move a great deal. By selecting projection images from a specific heart phase, a process known as EKG gating, the movement may be practically frozen. There are still smaller variances in the 3D position. In addition, the number of projection images available for a reconstruction is reduced by such EKG gating.
Tomographic image reconstruction is typically not possible under these conditions. As an alternative, symbolic 3D reconstructions are used. To create this type of symbolic 3D reconstruction, first of all, suitable 2D projection images are selected manually by a user, and individual vessels are segmented manually in the selected projection images. After a rough specification of an estimated vessel center line by a user, an exact center line is determined by a computing device. Thereafter, with the aid of the segmentation, the associated vessel edges are found and the vessel radii for this center line are computed.
To determine a 3D center line and a 3D vessel diameter for an individual vessel segment (e.g., a segment of the vessel between two branches or bifurcations in the vessel system) landmarks are detected automatically in the projection images. The landmarks are registered between different projection images, and information about the respective recording geometries of the projection images is additionally used.
The manual segmentation of projection images, as well as the specification of an approximate vessel center line for a relevant vessel are relatively complex. In addition, tight restrictions are imposed on the automatic detection of landmarks in the methods described, so that only individual, short vessel segments may be reconstructed.